1. Field of the Invention
This invention relates to a data recording apparatus having a variable recording speed for data.
2. Description of the Related Art
A data recording apparatus for recording digital data onto a magnetic tape as a recording medium has been conventionally known, such as, a data recording apparatus for recording data with high density using a digital video tape recorder of helical scan system.
FIG. 1 schematically shows the structure of a recording system of the above-described data recording apparatus. A signal processing circuit 6 treats data entered from an input terminal with signal processing for recording, and outputs the resulting signal as a digital recording signal to a recording amplifier 10. Speed information and a recording current for the digital recording signal are also entered to the recording amplifier 10 from a control circuit 7. The recording amplifier 10, which is a signal waveform shaping unit for recording data with the same characteristics at different speeds, is constituted by a class A linear amplifier. Frequency characteristics of a filter unit of this recording amplifier 10 are switched in response to the data rate.
In this recording amplifier 10, the input digital recording signal is transmitted to one of plural filters 22.sub.1, 22.sub.2, . . . , 22.sub.n in a filter unit 22. The filters 22.sub.1, 22.sub.2, . . . , 22.sub.n in the filter unit 22 are adapted for speed information fed from the control circuit 7. For example, the 1/1-tuple speed filter 22.sub.1 is adapted for a digital recording signal of normal data rate, that is, 1/1-tuple speed. The 1/2-tuple speed filter 22.sub.2 is adapted for a digital recording signal of a data rate 1/2 times the normal data rate. The 1/n-tuple filter 22.sub.n is adapted for a digital recording signal of a data rate 1/n times the normal data rate. The filters 22.sub.1, 22.sub.2, . . . , 22.sub.n in the filter unit 22 are correspondingly connected to fixed terminals 23.sub.1, 23.sub.2, . . . , 23.sub.n in a signal changeover switch 23, respectively.
In the signal changeover switch 23, the fixed terminals 23.sub.1, 23.sub.2, . . . , 23.sub.n are switched in accordance with the speed information, that is, the data rate selected and transmitted by the control circuit 7. The digital recording signal passing through the filter of the filter unit 22 connected to the selected fixed terminal is outputted through the signal changeover switch 23 to a class A amplifier 24.
The class A amplifier 24, supplied with the recording current from the control circuit 7, shapes a waveform of the input digital recording signal. The digital recording signal having its waveform shaped is outputted from the recording amplifier 10, and is recorded through a rotary transducer 8 into a magnetic recording medium, such as, a magnetic tape 30, by a recording head 9 rotated at a speed corresponding to the currently selected data rate.
In the above-described data recording apparatus, the rotation speed of the recording head 9 and the running speed of the magnetic tape 30 are controlled, so that data of variable data rate is recorded and reproduced. Specifically, the running speed of the magnetic tape 30 and the rotation speed of the recording head 9 are variably controlled to 1/1, 1/2, 1/4, 1/16 and 1/24 times the normal speed, so that information data having data rates of 88, 44, 22, 11, 5.50 and 3.67 Mbps, that is, a digital recording signal having maximum frequencies 44, 22, 11, 5.50, 2.75 and 1.84 MHz can be recorded and reproduced. That is, the information data recorded with the digital recording signal having the data rate of 88 Mbps, that is, the maximum frequency of 44 MHz, can be read out as information data having the data rate of 44 Mbps, that is, the maximum frequency of 22 MHz, when the speeds of the magnetic tape 30 and the recording head 9 are controlled to 1/2 times the normal speed. Thus, 1/2-tuple speed low-speed reproduction can be carried out.
The waveform of data before passing through the filter unit 22 is now described. FIG. 2A shows a waveform with 1/1-tuple data rate. FIG. 2C shows a waveform with 1/2-tuple data rate. FIG. 2E shows a waveform with 1/n-tuple data rate. FIGS. 2B, 2D and 2F show waveforms of the digital recording signal after passing the data through the filter unit corresponding to FIGS. 2A, 2C and 2E, respectively. As shown in FIGS. 2B, 2D and 2F, the same waveforms are produced by passing the data through the filter unit. Thus, the same waveform can be produced by passing a digital recording signal of any data rate through the filter unit 22.
FIG. 3 shows frequency characteristics of the filters in the filter unit 22. For example, frequency characteristics of the 1/1-tuple speed filter 22.sub.1 for a digital recording signal having 1/1-tuple data rate, that is, frequency f.sub.0, are indicated by RT.sub.1. Enhancement is carried out in a frequency band indicated by P. That is, frequency characteristics of the recording current with the 1/1-tuple data rate are such that decremented high frequency band is compensated by capacities of an output stage of the class A amplifier 24, wiring, the rotary transducer 8 and the recording head 9, inductance by the recording head 9 and wiring, and dumping resistance for restricting the resonance thereof.
Frequency characteristics of the 1/2-tuple speed filter 22.sub.2 for a digital recording signal having 1/2-tuple data rate, that is, frequency f.sub.0 /2, are indicated by RT.sub.2. Frequency characteristics of the speed filter for a digital recording signal having 1/4-tuple data rate, that is, frequency f.sub.0 /4, are indicated by RT.sub.3. Frequency characteristics of the speed filter for a digital recording signal having 1/8-tuple data rate, that is, frequency f.sub.0 /8, are indicated by RT.sub.4. Each filter also carries out peak shift correction.
Meanwhile, the recording amplifier 10 is the class A linear amplifier, and therefore consumes a large quantity of electric power.
In addition, the recording amplifier 10 requires the number of filters corresponding to the number of types of data rates. The filters of the filter unit 22 have high operation frequencies, and cannot be constituted by active filters. Therefore, the circuit scale is enlarged.
Thus, it is difficult to realize continuous variable speed.